International patent application PCT/IB00/01571 published under WO 01/32537A1 describes a conveyor idler with a braking mechanism within the drum of the conveyor idler. The braking mechanism permits the drum to rotate in a forward direction but not in a reverse direction. The braking mechanism consists of a brake guide fixed to the shaft of the conveyor idler. The brake guide has recesses on its circumference. On each of the recesses a ball bearing is located. One of the ball bearings becomes wedged between the inner surface of the drum and its recess on the brake guide when an attempt is made to rotate the drum in the reverse direction thereby preventing the drum from being rotated in the reverse direction. The conveyor idler suffers from the disadvantage that generally only one of the ball bearings becomes wedged between the drum and the brake guide and therefore that all the locking torque is transferred through only one ball bearing. In addition, the brake guide is relatively large and the ball bearings contact the drum even when it rotates in the forward direction. This contact results in the generation of noise and in wear.